I don't know why you're saying it's an invalid expression. Help me

Question

kubel 2023-9-12

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编辑： John D'Errico 2023-9-12

clear all; close all;
x=linspace(-2*pi,2*pi,100);
y1=sin(x^2); 
y2=cos^2(x);
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.
figure(1)
plot(x,y1,x,y2)
grid on
title('HW#1 test -2_pi and 2_pi')
xlabel('-2pi < x < 2pi')
ylabel('sin(x^2) and cos(x)^2')
legend('y = sin(x)','y = cos(x)')

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Answer 1

Matt J 2023-9-12

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编辑：Matt J 2023-9-12

在 MATLAB Online 中打开

Perhaps you intended to have this,

y1=sin(x.^2); 
y2=cos(x).^2;

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kubel 2023-9-12

Oh, thank you so much

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Answer 2

John D'Errico 2023-9-12

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编辑：John D'Errico 2023-9-12

在 MATLAB Online 中打开

You NEED to learn about the dotted operators, thus .*, ./, and .^ operators.

When x is a vector, for example, this:

x = 1:5
x = 1×5
     1     2     3     4     5

So we see it is a row vector. MATLAB has special uses for ^, * and / that apply to linear algebra, vectors and matrices. So if you want only to square the elements of x,

x.^2
ans = 1×5
     1     4     9    16    25

The dotted operator tells MATLAB to square EACH element of the result. Similarly, we could do this

x.*x
ans = 1×5
     1     4     9    16    25

Again, multiply each pair of elements in turn.

But when you did this:

x^2
Error using ^
Incorrect dimensions for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To operate on each element of the matrix individually, use POWER (.^) for elementwise power.

It generates an error.

I would strongly suggest the MATLAB Onramp tutorials.